When waterfall was going out, and Xtreme Programming was coming in, you heard that kind of phrase a lot. If we don't have waterfall, then what? If we don't have functional requirements then what? etc etc.
This is a good article. The recommendations fall in line with JP Lewis' "Large Limits to Software Estimation".
http://scribblethink.org/Work/kcsest.pdf
http://scribblethink.org/Work/Softestim/softestim.html